Shared Folders: make rm/rmdir work with Solaris guests on Windows hosts

Networking: ﬁxed the problem with blocked receiving thread when a broadcast packet arrives too early to be handled by uninitialized e1000 adapter.

Networking: ﬁxed the problem that caused host freezes/crashes when using bridged mode with host’s interface having RX checksum ofﬂoading on (bug #3926 and related). Fixes problems with TX ofﬂoading as well (bug #3870)